Cross-Linking Polymerizations in Two-Dimensional Assemblies

Polymerization of monomeric lipids in an assembly proceeds in a linear or cross-linking manner depending on the number of polymerizable groups per monomeric lipid. Lipids that contain a single reactive moiety in either of the hydrophobic tails or associated with the hydrophillic head group yield linear polymers. Polymerization of lipids with reactive groups in each hydrophobic tail generally yield cross-linked polymeric networks. This report describes three approaches to the characterization of the gel point for polymerizations constrained by the two-dimensional nature of lipid bilayers. The gel point for two-dimensional lipid assemblies was determined by correlation of the onset of significant changes in the physical properties of the polymerized bilayers with the bilayer composition. The properties examined in this study were the lateral diffusion of a small molecule probe of the bilayer, the stability of polymerized bilayer vesicles in the presence of surfactants, and the solubility of lipid polymers i...